Hi all, has anyone ever seen a VFD (vacuum fluorescent display) failure in which half the display is very dim and the other half looks good? I have this 16 character (16 segments) 1 row display and the first 8-10 characters have a normal brightness, the rightmost ones are very dim, barely readable. I first suspected a problem with the filament supply, but swapping the filament pins has no effect, so I'm a bit puzzled. Waveforms look identical on all the 16 grids too. Unfortunately I have no schematic of this instrument (digelec 824 eeprom programmer), nobody else in the world seems to have this programmer also, so I could not ask anyone for some quick waveform comparison. I'm starting to suspect a bad VFD but I can't imagine how would it fail like this. Part of the filament supply is made with a NE555 that's getting quite hot and also a 120 ohm 1/4W resistor near it gets too hot to touch, but all components I could test looks ok. I swapped the 555 and it doesn't make any change. If I leave the 555 out, the display has no filament supply. Any hint is really welcome. Regards
Frank IZ8DWF